Connections between optical transmission paths may be made by terminating optical fiber with plugs and by holding two such plugs which terminate optical fibers to be connected in predetermined positions with respect to each other. One such connection arrangement is referred to as a biconic connector which is disclosed in U.S. Pat. No. 4,512,630 which issued on Apr. 23, 1985 in the name of P. K. Runge. In it, each optical fiber is terminated in a plug having a truncated conical shape. Two such plugs are disposed in a biconical sleeve with small diameter end portions of the plugs being adjacent to a center plane. Another optical fiber connector is AT&T's ST.RTM. connector which comprises a cylindrically shaped ferrule or plug that terminates an optical fiber. The plug is disposed within a cap and is biased outwardly. Two such plugs may be inserted into a sleeve having a longitudinal slot therein with the end faces of the plugs being in contact with each other or spaced apart by an attenuator.
In order to achieve low loss, low reflectance connections, the end faces of the two plugs in which the optical fibers terminate need to have surfaces which are substantially normal to the longitudinal axes of the plugs and which may have optical fibers protruding slightly therefrom and being smoothly polished. Otherwise, the surfaces may be skewed to each other and/or surface roughness may cause the end faces of the fiber cores not to be substantially in engagement with each other or in engagement with an attenuator that may be disposed between the end faces.
Also, an end portion of each optical fiber which is terminated by a plug needs to be polished. After an optical fiber has been inserted into a passageway of the plug, an end portion of the fiber which extends beyond the end face of the plug is cleaved. This is a relatively rough, imprecise operation which leaves a portion of fiber extending beyond the end face of the plug. The protruding end must be polished so that an end face of the fiber is coplanar with or protrudes slightly from the end face of the plug. Such an operation must be carried out carefully to avoid fracturing the length of fiber which remains after the cleaving operation.
In the prior art, polishing of end faces of connector plugs and fiber has been accomplished manually. A connector plug to be polished is mounted in a fixture and the fixture is moved in oscillating circular patterns with the end face of the fiber and subsequently the plug in engagement with a polishing surface of a predetermined grit size. Such a fixture which may be used to polish an end face of a truncated conically shaped connector plug is disclosed in U.S. Pat. No. 4,539,776 which issued on Sep. 10, 1985 in the name of F. R. Weaver.
The manual polishing of fiber and connector plug end faces is not without problems. It should be apparent that such a procedure is subject to operator variations in pressure applied to the fixture and hence that between grit of the polishing surface and the end faces. Also, the length of time, the motion and the path along which the plug traverses may vary from plug to plug thus producing inconsistent results in fiber end face protrusion and extent of polish.
Also available in the prior art is apparatus for gang-polishing a plurality of connector plugs. Each of a plurality of plugs to be polished is mounted in a nest of a clamping ring. Then the clamping ring is moved desirably to cause ends of fibers protruding from the plugs to engage a polishing surface. The problems with such an apparatus are twofold. One problem is that when the fibers are cleaved, the length of fiber that extends beyond an end face of the plug varies significantly from plug to plug. When a plurality, for example, eight or twelve, are gang-polished, the fibers extending from several of the plugs may be longer and hence experience greater pressure as forces are applied to the clamping ring for the plurality of plugs. This greatly increases the possibility of cracking those fibers which extend farther from associated plug end faces than others. Secondly, the plugs may vary in length and yet be within prescribed tolerance limits. As a result of the variations in plug length, some of the plugs may be under-polished whereas others may be over-polished.
The last described apparatus clearly is a step in the right direction if plug type optical fiber connectors are to enjoy widespread use in field splicing operations. Just as clearly, such an apparatus is not totally satisfactory because of its inability to compensate for variations in dimensional tolerances.
What is needed and what seemingly is not provided for in the prior art are methods and apparatus for preparing an end face of a ferrule type connector plug adapted to receive an end portion of a length of optical fiber to facilitate an optical connection with another plug-terminated optical fiber. Further, what is sought are methods and apparatus for the simultaneous treatment of fibers which extend from end faces of a plurality of cylindrically shaped connector plugs with the capability of being used in the field by craftspersons and with the capability of compensating for dimensional variations in lengths of the plugs and initial fiber protrusions.